An electronic delay detonator has heretofore been known which allows an energy charging circuit to store therein electrical energy supplied from a blasting machine, is activated in response to the stored electrical energy and performs switching after a lapse of a desired delay time.
Prior arts of the electronic delay detonator have been proposed as examples as follows:
(i) A technique for controlling an ignition time by using a charge time constant of an RC circuit as a reference is disclosed in Japanese Patent Application Laid-Open Nos. 83200/1983, 91799/1987, etc. PA1 (ii) A technique for controlling an ignition time with extremely high time accuracy by using a characteristic frequency of a solid oscillator such as a quartz oscillator as a reference is disclosed in U.S. Pat. No. 4,445,435, DE 3,942,842, Japanese Patent Application Laid-Open No. 79797/1993, WO95/04253, etc. PA1 (a) A structure in which an electronic timer is inserted into a housing of an electric detonator and sealed with epoxy or a composition of epoxy with elastomer; PA1 (b) A structure cast-sealed with a thermoplastic resin such as polystyrene or polyethylene; PA1 (c) A structure in which a substrate is fixed to a case by an O-ring; and PA1 (d) A structure in which an electronic timer is directly inserted into a plastic case and a vacant space is defined between the case and the electronic timer. PA1 where t: ignition time interval PA1 (1) A mode where the electronic delay detonator is subjected to compression in all the directions through a spring water expected to be produced at a blasting site; PA1 (2) A mode where the electronic delay detonator is expelled by vibrations in an elastic range of rock so that displacement acceleration is produced; PA1 (3) A mode where explosive gas enters through a crack of rock so that compression applied from one direction or displacement acceleration is produced in the electronic delay detonator; and PA1 (4) A mode where the rock is displaced by destruction so that the electronic delay detonator is subjected to compression by the displaced rock. PA1 an energy charging circuit for storing electrical energy supplied from a power supply; PA1 a delay circuit for determining a time period by using the electrical energy stored in the energy charging circuit to thereby output a trigger signal; and PA1 a first switching circuit for supplying the electrical energy stored in the energy charging circuit to the ignition element in response to the trigger signal, PA1 wherein to an impact externally applied to the electronic delay detonator, a lower limit of an impact value in an induced detonation range of the electric detonator substantially overlaps with an upper limit of an impact value in a range in which the electronic timer is operable. PA1 an energy charging circuit for storing electrical energy supplied from a power supply; PA1 a delay circuit for determining a time period by using the electrical energy stored in the energy charging circuit to thereby output a trigger signal; and PA1 a first switching circuit for supplying the electrical energy stored in the energy charging circuit to the ignition element in response to the trigger signal, wherein the delay circuit comprises: PA1 an energy charging circuit for storing electrical energy supplied from a power supply; PA1 a delay circuit for determining a time period by using the electrical energy stored in the energy charging circuit to thereby output a trigger signal; and PA1 a first switching circuit for supplying the electrical energy stored in the energy charging circuit to the ignition element in response to the trigger signal, wherein the electronic timer comprises: PA1 an energy charging circuit for storing electrical energy supplied from a power supply; PA1 a delay circuit for determining a time period by using the electrical energy stored in the energy charging circuit to thereby output a trigger signal; and PA1 a first switching circuit for supplying the electrical energy stored in the energy charging circuit to the ignition element in response to the trigger signal, wherein the electronic timer is housed within a cylinder having impact resisting properties, and a space defined between the electronic timer and a wall of the cylinder is filled with a viscoelasticity material. PA1 an energy charging circuit for storing electrical energy supplied from a power supply; PA1 a delay circuit for determining a time period by using the electrical energy stored in the energy charging circuit to thereby output a trigger signal; and PA1 a first switching circuit for supplying the electrical energy stored in the energy charging circuit to the ignition element in response to the trigger signal, wherein the electronic timer is housed within a cylinder having impact resisting properties, only a periphery of the energy charging circuit is covered with one of a foamed resin and a gel-like substance material whose needle penetration ranges from 10 to 100, and an overall space defined between the electronic timer and a wall of the cylinder is filled with a viscoelasticity material. PA1 a reference pulse generator circuit for generating a reference pulse signal based on the count period; and PA1 a main counter circuit for outputting the trigger signal when the main counter circuit has counted the reference pulse signal by preset times. PA1 a circuit for generating a count period creation start signal and a count period creation end signal when the generating circuit has counted the pulse outputted from the first oscillator circuit by first and second preset times; and PA1 a periodic counting data circuit for starting the counting of the pulse outputted from the second oscillator circuit upon receiving the count period creation start signal, terminating the counting of the output pulse of the second oscillator circuit upon receiving the count period creation end signal, and then fixing the result of the counting as a count period. PA1 means for producing, as the reference period, first to nth (.gtoreq.2) fixed time intervals whose minimum fixed time interval is equal to the minimum ignition time interval and which are predetermined and different from each other, using the pulse generated by the first oscillator circuit as a reference, and means for producing and latching the first to nth (.gtoreq.2) count periods in accordance with the first to nth fixed time intervals using a pulse train generated by the second oscillator circuit as a reference, PA1 and wherein the trigger signal generating circuit comprises: PA1 a first fixed time interval producing counter for counting a pulse train generated from the first oscillator circuit during the first fixed time interval; and PA1 second through nth fixed time interval producing counters for respectively counting the pulse train generated from the first oscillator circuit during the second through nth fixed time intervals. PA1 latch circuits for latching the first to nth fixed time intervals; PA1 first to nth separating counters which is set with first to nth fixed time intervals latched in the latch circuits individually, the first to nth separating counters respectively counting the pulse train generated by the second oscillator circuit and outputting pulse signals each count-up time; and PA1 first to nth counters for counting pulses outputted from the first to nth separating counters each time the first to nth separating counters count up, the first to nth counters being activated in serial so as to release the (m-1) th counter from the reset state in response to the count-up of the mth (.ltoreq.n ) counter.
In general, each of these electronic delay detonators comprises an electronic timer 100 supplied with electrical energy from a blasting machine 10 and an electric detonator 200 as shown in FIG. 1. The electronic timer 100 includes an energy charging circuit 120, a delay circuit 30 and an electronic switching circuit 140. In blasting, the electronic timer 100 is supplied with the electrical energy from the blasting machine 10, stores the electrical energy in the energy charging circuit 120, and then, drives the delay circuit 30 based on the electrical energy stored in the energy charging circuit 120 after completion of the supply of the electrical energy from the blasting machine 10. After a predetermined delay time has elapsed, the delay circuit 30 closes the electronic switching circuit 140 so that the electrical energy stored in the energy charging circuit 120 is supplied to the electric detonator 200, whereby the electric detonator 200 is fired.
Thus, when the electronic timer 100 including the delay circuit 30 is deactivated for some causes, generally, damage by an impact, the electric detonator 200 is not fired. Therefore, structures for protecting the electronic timer against the impact grow in importance. As these techniques, there have heretofore been known ones disclosed in Japanese Patent Application Laid-Open Nos. 35298/1982, 290398/1988 and 158999/1987, Japanese Utility Model Application Laid-Open No. 31398/1989, etc., for example. The following structures have been disclosed in these gazettes.
Major uses of the aforementioned electronic delay detonator are for reduction in ground vibration or noise produced due to blasting. As described in Japanese Patent Application Laid-Open No. 285800/1989, it is however necessary to meet the following condition in respect of the accuracy of an ignition time with a view toward achieving these objects: EQU t/.sigma..gtoreq.10
.sigma.: standard deviation of variation in ignition time interval PA2 a first oscillator circuit using a characteristic frequency of a quartz oscillator as a reference; PA2 a second oscillator circuit having impact resisting properties; PA2 a count period producing circuit for producing one or a plurality of count periods by using pulses of the second oscillator circuit so that a count period coincides with a reference period produced by pulses of the first oscillator circuit; and PA2 a trigger signal generating circuit for generating and outputting the trigger signal based on the count period. PA2 a malfunction detecting circuit for detecting a malfunction of circuit elements, the malfunction occurring when the circuit element is subjected to an explosive shock, and the malfunction detecting circuit outputting a malfunction detecting signal; PA2 a forced trigger circuit for outputting a forced trigger signal in response to the malfunction detecting signal; and PA2 a second switching circuit for supplying the ignition element with the electrical energy stored in the energy charging circuit in response to the forced trigger signal. PA2 first to nth separating means for respectively separating predetermined delay time intervals in reverse order by predetermined times in accordance with the first through nth count periods using a pulse train generated by the second oscillator circuit as a reference; and PA2 means for generating the trigger signal when the predetermined delay time intervals have been separated by the predetermined number of times at the first count period by the first separating means.
It is desirable that since the ignition time interval t is often set to within 10 ms, the standard deviation .sigma. of the ignition time interval should be limited so as to fall within at most .+-.1 ms.
In actual blasting work, a plurality of explosives inserted in electronic delay detonators are used and charged into their corresponding explosive boreholes defined therein based on predetermined blasting patterns. Thereafter, the explosives are successively detonated to fracture such as rock with predetermined time differences. Therefore, these explosive boreholes are expected to be adjacent to each other at a much shorter distance according to the blasting patterns. It is also apprehended that the explosives and electronic delay detonators will be subjected to a violent blasting shock of the adjacent boreholes before their own firing. Particularly when the blasting work is carried out for tunnel digging, the bootlegs of the adjacent boreholes are defined so as to be close to each other to improve fracturing effects, and the interval between the bootlegs often reaches 20 cm or less in the case of a fracturing method called "V cut".
Further, the following various shock modes are considered as examples of explosive shocks that the electronic delay detonator undergoes before its own firing.
The degree of each shock differs according to the quantity of explosives in the source of explosion and the condition of the rock. However, the degree of the shock is considered to reach pressures of 30 MPa to 70 MPa or shock acceleration of several tens of thousands of G to several hundreds of thousands of G at a distance of about 20 cm from exploding site.
In this case, the electronic delay detonator will be subjected to an extremely large explosive shock and hence the conventional techniques referred to above have much difficulty in completely eliminating misfire of an electric detonator.
In contrast to this, since all the ignition charges of conventional individual electric detonators using not the electronic timer but delay charges, are simultaneously fired even when the conventional electric detonators are subjected to the aforementioned shocks, the detonators are little misfired even if a detonation force of each electric detonator is reduced (imperfectly detonated). Further, when the shocks that such electric detonators undergo, are so violent, the ignition charges, primary explosives or base charges are subjected to compression or impact so that the electric detonators are often sympathetically detonated prior to the detonation using the delay charges (see FIG. 2A).
In the conventional electronic delay detonator using the electronic timer, however, when the electronic delay detonator is subjected to the violent explosive shock, i.e., the compression or displacement acceleration, there exists a range in which the electronic timer produces damage under an impact force having a level lower than an impact level at which the electric detonator reaches the sympathetic detonation. Further, a misfire range in which the electric detonator is not fired, exists between a range in which the electric detonator reaches the sympathetic detonation and a range in which the electronic timer is operable.
Particularly in the case of an electronic delay detonator having a high-accuracy electronic timer using a quartz oscillator, a crystal rod is bent due to displacement acceleration. With marked bending, the crystal rod collides with a case cylinder, so that the crystal may cause damage.
Thus, the quartz oscillator becomes a big factor that lowers an impact resisting level under which the quartz oscillator avoids damage as compared with other parts, and reduces the operating range of the electronic timer to thereby cause misfiring (see FIG. 2B).
According to the already-described WO95/04253, the technique has been proposed that an RC oscillator circuit is activated in cooperation with a quarts oscillator circuit, and the operation of the quartz oscillator circuit is changed-to that of the RC oscillator circuit when the quartz oscillator fails. However, the proposed technique is accompanied by problems that when a hybrid integrated circuit (HIC) including the RC oscillator circuit is subjected to such a shock that will cause damage, a misfire range cannot be avoided from occurring and the accuracy of operation subsequent to the substitution of the RC oscillator circuit is reduced.